1. Field of the Invention
The present invention relates to a substrate having a fluorescent member used in an electronic display device which takes advantage of electron beam excitation. In addition, the present invention relates to an image display apparatus and image receiving and displaying apparatus using the substrate having a fluorescent member.
2. Description of the Related Art
In a conventionally known image display apparatus using an electron-emitting device which emits electrons by applying an electric field (hereinafter referred to as FED), a gap between a cathode substrate on an electron source side and a front substrate being an anode is limited generally to several mm for reasons of beam convergence and others. The small gap imposes considerable constraint on electric discharge resistance. Therefore, an accelerating voltage of as high as 25 kV used in a cathode ray tube (hereinafter referred to as CRT) can not be applied. Even an FED, generally referred to as being of high voltage type, typically uses an accelerating voltage of 15 kV or lower. For this reason, a diffusion length over which an electron enters a fluorescent-member layer is shorter compared with the case where a CRT is used, which requires drive by a high electric-charge density, for example, by a subsequent drive using high current electron beams to realize the luminance equivalent to that obtained by a CRT. This requires a fluorescent member to secure a luminance linearity when a high electric-charge density is applied.
A group of zinc sulfide fluorescent members which have long been used in a CRT and referred to as P22 is typically used as a present practically applicable fluorescent member excited by electron beams. The P22 fluorescent member which have long been used in a CRT is typically used even in the FED as described in Japanese Patent Publication No. S63-039982. The zinc sulfide fluorescent member, however, is as long as several tens of micro seconds in luminescent decay time because the member emits light by a donor-accepter recombination in a host material formed by exciting energy. Furthermore, the zinc sulfide fluorescent member is lower in an optimum luminescence center concentration in consideration of influence such as density quenching than inner transition phosphor doped with rare earth metal. This tends to comparatively easily cause the saturation of an excited luminescence center at a high electric-charge density area, leading to an insufficient luminance linearity not to provide a satisfactory luminance.
Various kinds of proposals have been put forth to solve these problems. Japanese Patent Application Laid-Open No. H06-248262 discloses a method of improving a blue luminance using a mixture of fluorescent members different in their characteristics. Specifically, a mixed blue light-emitting fluorescent member has been proposed which includes at least one fluorescent member selected from the group including terbium activated yttrium aluminum garnet fluorescent member Y3(Al,Ga)5O12:Tb, terbium activated silicic acid yttrium fluorescent member Y2SiO5:Tb, terbium activated oxychloride lanthanum fluorescent member LaOCl:Tb, which are 20% or less by weight with respect to the total weight of the mixed fluorescent member, and silver-aluminum coactivated zinc sulfide fluorescent member ZnS:Ag,Al as a remaining portion of the total weight.
Japanese Patent Application Laid-Open No. 2004-339293 discloses a method of using a mixture of at least two kinds of fluorescent members selected from hexagonal crystal ZnS:Ag,Al, hexagonal crystal ZnS:Cu,Al and hexagonal crystal ZnS:Tm,Li.